The invention relates to a tool for the setting of a plastic rivet used to conjugally secure a plurality of elements.
The prior art teaches the setting of a thermoplastic rivet by means of a tool employing a die to exert a compressive axial force on the end thereof so as to form the plastic to the shape of the die. Additionally, the prior art teaches the setting, or more accurately, the softening, head forming and complete polymerization, of a thermoset plastic rivet such as the "Composite Rivet" disclosed in U.S. No. 4,478,544, issued Oct. 23, 1984, and assigned to the assignee of the instant invention, by the following method: heat is applied to initiate softening and full polymerization of the "B" stage head forming portion(s) of the rivet, to be followed immediately thereafter by head forming, either by a mandrel having a head forming anvil in the case of a blind rivet, or by a heading tool comprising a die. Because of the difficulty of applying the heat to the thermoset rivet at the proper instant prior to and during the head forming operation, resort has been made to using plastics which remain as a "B" stage thermoset resin only at relatively low temperatures. The removal of such a rivet from the low temperature environment to ambient temperature conditions imparts sufficient heat thereto to initially soften, and eventually cause complete polymerization of, the rivet. A change in the rate of heat transfer to the rivet therefore has a marked effect on the physical properties of the rivet and the "setting" process.
The aforementioned teachings do not disclose a tool having easily removable heated head forming dies having a spring-biased lost motion connection therebetween so as to prevent damage to the elements being joined upon initial tool clamping and during maintenance of tool clamping force during polymerization of the rivet.